1. Field of the Invention
The present invention relates to a scanning device for a color optical reader, specifically, a high speed single-pass scanning device that can reduce the size of a color optical reader.
2. Brief Description of Prior Art
The scanning methods for a conventional color optical reader can be classified as follows:
1. A Single-Charge-Coupled-Device (CCD) 10 illuminated with multiple color light sources (usually red, green and blue light sources). As in FIG. 1, the light from light source 12 is reflected by mirror 13 to fall on CCD 10 through the lens 11.
2. A Single CCD 10 with a white light source 12 and filtered with multiple color filters, as in FIG. 2.
3. A Multiple CCD 10A, 10B, 10C with prism 10D illuminated by a white light source 12, as in FIG. 3.
4. A Color CCD 10 illuminated by a white light source 12, as in FIG. 4.
A conventional scanning device as in FIG. 1, because of its multiple light sources, it is quite large and not easily reduced in size. To complete the scanning process, the red, green and blue light sources must be turned on and off periodically. For most light sources, to obtain the intense and stable light needed for high quality color scanning, it requires the passage of a relatively long time and will thus reduce the scanning speed accordingly.
For the scanning device shown in FIG. 2 in which a color filter module 14 is set in front of the lens, the entire optical and mechanical structure becomes increasingly complicated and the size of this kind of scanning device will grow even larger. This kind of scanning device uses mechanical methods to periodically position the red, green and blue filters in front of the lens. Because mechanical operations have a slow response speed, we cannot achieve high speed color scanning.
The scanning device shown in FIG. 3 can obtain high speed color scanning because three CCD's 10A, 10B and 10C are used to simultaneously detect the red, green and blue light respectively. But the need for 3 CCD's makes this kind of device much more expensive than single CCD counterparts. The prism needed also makes the optical and mechanical design much more complicated.
As for the scanning device shown in FIG. 4, a color CCD is used so extra filters or a prism is not required, and a minimum size can be achieved. But because the color CCD simultaneously outputs red, green and blue signals, the cost of the image processing circuitry will increase considerably.